THe problem with the E46s is ROOM and ITBs.

Intake manifold wise it will be a pain because of the sensor locations and the fact that it comes with ITBs from the factory. I wouldnt mess with custom intake manifold on that car, id focus on running the IC piping to a plenum that encompasses the ITBs.

Turbo manifold wise, Autofab or TurboDave would prob be the places to look into. Daves done some oddball cars like a S60R volvo and such so im sure he could figure something out.

It wont be cheap though, those cars cost $$$$$. Talk to BOKI on here, he is turboing his e46 and hes been compiling stuff for 2+Years